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Preparation Of Metal Halide Phosphor Particles Of Selected Particle Size Range With Improved Powder Flowability - Patent 5360578


DESCRIPTION1. Field of the InventionThe present invention relates to a method for preparing metal halide phosphor particles of a selected particle size range having their surface coated for improving their flowability, i.e. powder fluidity, and also relates to the use of saidphosphor particles in the production of radiographic phosphor screens.2. Background of the InventionIn radiography the interior of objects is reproduced by means of penetrating radiation, which is high energy radiation also known as ionizing radiation belonging to the class of X-rays, gamma-rays and high-energy elementary particle radiation,e.g. beta-fays, electron beam or neutron radiation. For the conversion of penetrating radiation into visible light and/or ultraviolet radiation luminescent materials, called phosphors, are used.In a conventional radiographic system an X-ray radiograph is obtained by X-rays transmitted imagewise through an object and converted into light of corresponding intensity in a so-called intensifying screen (X-ray conversion screen) whereinphosphor particles absorb the transmitted X-rays and convert them into visible light and/or ultraviolet radiation to which a photographic film is more sensitive than to the direct impact of X-rays.In practice the light emitted imagewise by said screen irradiates a contacting photographic silver halide emulsion layer film which after exposure is developed to form therein a silver image in conformity with the X-ray image.More recently as described e.g. in U.S. Pat. No. 3,859,527 an X-ray recording system has been developed wherein photostimulable storage phosphors are used having in addition to their immediate light emission (prompt emission) on X-rayirradiation-the property to store temporarily a large part of the X-ray energy. Said energy is set free by photostimulation in the form of fluorescent light different in wavelength from the light used in the photostimulation. In said X-ray recordingsystem the light emitted on photos

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